Consistent reactor-core versions

Previously the IDE (STS) was resolving a different reactor-core
version (3.0.0.BUILD-SNAPSHOT) than the build (3.0.0.RELEASE). This
discrepancy was due to the fact that reactor-netty now brings in
reactor-core 3.0.0.RELEASE. Gradle's version conflict resolution is to use
the latest version. However, the optional dependency on reactor-core
3.0.0.BUILD-SNAPSHOT was making the build path of the IDE use the SNAPSHOT.

This fix leverages a resolutionStrategy to ensure a consistent version of
reactor-core is used throughout the entire project. It also bumps up the
reactor-core version to 3.0.0.RELEASE to be consistent with reactor-netty.
Care is taken to only change 3.x vesion since 2.x is still used within
the codebase.

build.gradle

@@ -74,7 +74,7 @@ configure(allprojects) { project ->
 	ext.protobufVersion        = "3.0.0"
 	ext.reactivestreamsVersion = "1.0.0"
 	ext.reactorVersion         = "2.0.8.RELEASE"
-	ext.reactorCoreVersion     = '3.0.0.BUILD-SNAPSHOT'
+	ext.reactorCoreVersion     = '3.0.0.RELEASE'
 	ext.reactorNettyVersion    = '0.5.0.BUILD-SNAPSHOT'
 	ext.romeVersion            = "1.6.0"
 	ext.rxjavaVersion          = '1.1.9'
@@ -116,6 +116,11 @@ configure(allprojects) { project ->
 				details.useVersion nettyVersion
 			}
 		}
+		resolutionStrategy.eachDependency { DependencyResolveDetails details ->
+			if (details.requested.name == 'reactor-core' && details.requested.version.startsWith('3.')) {
+				details.useVersion reactorCoreVersion
+			}
+		}
 	}
 
 	compileJava.options.encoding = 'UTF-8'